The present invention relates to hand tools for removing burrs, from a drilled hole and in particular, to tools that rotate as a handle is reciprocated and a shaft retracts and extends.
After drilling a hole, a machinist will routinely insert and twist a deburring tool in the hole. While the hand tool is quick because it is self-centering, manual operations on many holes can be fatiguing and produce inconsistent results. Alternatively, a drill press fitted with a deburring tool can be carefully centered over the hole and carefully pressed into the hole to be deburred. A drill press, however, is not self-centering and can produce excessive pressure that enlarges the hole unacceptably. Either operation is tedious and time consuming.
A known screwdriver (sometimes referred to as a "Yankee" screwdriver) has a shaft with axial grooves and a hollow handle. When pushing the handle towards a workpiece, a key inside the handle can ride on a spiral groove and turn the shaft and drive a screw. These known hand tools have a reversible setting so the tool can rotate in either direction. These known hand tools turn their shaft typically when the handle is thrust towards the workpiece and the spirally grooved shaft retracts into the handle.
If "Yankee" screwdrivers were fitted with a deburring tool, they would not operate satisfactorily. Such a screwdriver normally turns when the handle is pressed towards the workpiece and the shaft retracts. Consequently, the lightest amount of pressure occurs at the beginning of the deburring stroke, followed by pressure that gradually increases to the maximum at the end of the stroke when the shaft is fully retracted into the handle. This operation is precisely the opposite of what is needed. The pressure should decrease during the cutting cycle so the countersink will gradually stop cutting, and begin smoothing and polishing the chamfered surface. Applying maximum pressure at the end of the deburring stroke tends to finish the stroke with gouges left by the deburring tool itself.
The screwdriver shaft in U.S. Pat. No. 2,646,687 can idle when the handle is pushed towards the workpiece but rotate as the handle withdraws and the shaft extends from the handle. This reference, however, does not suggest using a deburring tool instead of a screwdriver blade. Furthermore, the reference does not suggest setting the shaft pitch and setting the springs so the decreasing pressure stops the cutting action and smooths the chamfered surface, thus enhancing its deburring capability. See also U.S. Pat. Nos. 1,744,921; 1,937,645; and 2,337,514.
Accordingly, there is a need for a simple deburring hand tool that is self-centering, self-contained, and that decreases its pressure toward the end of the operating stroke to smooth the aperture without leaving gouges.